Note 1 - Organization and Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands					1 Months Ended		3 Months Ended				6 Months Ended			12 Months Ended		16 Months Ended	17 Months Ended
		Jun. 11, 2024	Mar. 07, 2023	Oct. 29, 2021	Jul. 25, 2024	Jun. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024		Jun. 30, 2023	Dec. 31, 2023		Jun. 30, 2024	Mar. 30, 2023
Stock Issued During Period, Shares, New Issues (in shares)	[1]										13,480,458			15,880,039
Stock Issued During Period, Value, New Issues							$ 100,698	$ 13,109	$ 47,355	$ 31,657	$ 113,807	[1],[2]		$ 159,438	[1],[2]
Proceeds from Issuance of Common Stock											$ 113,807		$ 79,012
October 2021 Equity Distribution Agreement [Member]
Equity Agreement, Maximum Number of Shares Issuable (in shares)				250,000,000
Stock Issued During Period, Shares, New Issues (in shares)																	9,742,188
Stock Issued During Period, Value, New Issues																	$ 151,800
Proceeds from Issuance of Common Stock																	$ 149,300
March 2023 Equity Distribution Agreement [Member]
Equity Agreement, Maximum Number of Shares Issuable (in shares)			250,000,000
Stock Issued During Period, Shares, New Issues (in shares)																24,675,497
Stock Issued During Period, Value, New Issues																$ 228,800
Proceeds from Issuance of Common Stock																$ 225,000
June 2024 Equity Distribution Agreement [Member]
Equity Agreement, Maximum Number of Shares Issuable (in shares)		250,000,000
Stock Issued During Period, Shares, New Issues (in shares)						1,995,000
Stock Issued During Period, Value, New Issues						$ 16,900
Proceeds from Issuance of Common Stock						$ 16,600
June 2024 Equity Distribution Agreement [Member] | Subsequent Event [Member]
Stock Issued During Period, Shares, New Issues (in shares)					6,514,200
Stock Issued During Period, Value, New Issues					$ 55,500
Proceeds from Issuance of Common Stock					$ 54,600

[1] The Company has entered into eleven equity distribution agreements, ten of which have either been terminated because all shares were sold or were replaced with a subsequent agreement.

[2] Net proceeds are net of the underwriters’ discount, if applicable, and other offering costs.